Satellite-based navigation systems are becoming increasingly important in a wide range of applications, including handheld devices for position determination, in-car navigation support, and so on. The main Global Navigation Satellite Systems (GNSS) in service at present is the global positioning system (GPS) operated by the United States Department of Defense. Numerous other satellite navigation systems like European counterpart satellite navigation system, named Galileo, GLONASS (Russia), Compass (China), IRNSS (India) and QZSS (Japan) are currently under modernization or under deployment.
The basic components of a navigation signal as emitted by a satellite or a pseudolite are a spreading code (also referred to as a positioning, synchronization or ranging code), which is combined with the spreading symbol setting the modulation waveform and the navigation data. The resulting combination is then modulated onto a carrier at a set frequency for transmission to earth. Each emitter generally transmits at multiple frequencies, which can help to compensate for ionospheric effects, to improve accuracy and to broadcast more data. In some cases, multiple signal channels may be modulated onto a single carrier via some appropriate multiplexing scheme.
For example, GPS satellites transmit data along an L1 frequency and an L2 frequency. The L1 frequency is known as the course acquisition (C/A) code. The C/A code is available for civilian use and is a 1.023 MHz PRN code, which repeats its 1023 bits each millisecond. Each satellite transmits a unique PRN code so that GPS receivers can identify each satellite based on the PRN code received from a given satellite.
The spreading sequences used as the C/A codes in GPS belong to a unique family of sequences, referred to as Gold codes that are the sum of two maximum-length sequences. In other words, the C/A code, which are unique for each GPS satellite, are pseudo-random Gold codes comprising a repetition of a 1023 bits, or “chips,” with a transition rate of 1.023 MHz, and are often indicated in short as PRN. Moreover, the PRN codes transmitted by the GPS satellites are deterministic sequences with noise like properties. Each C/A code is generated using different initial tapped linear feedback shift register (LFSR) setting. It may therefore be desirable to have a system and method that optimizes signal functions and PRN code generations by reducing hardware components and the processing time, while increasing the speed, flexibility and efficiency of a GNSS system.